Contact positioning arrangement for quick break mechanism of load tap changing transformer



Dec 1%, 3956 w. c. SEALEY 2,774,830

CONTACT POSITIONING ARRANGEMENT FOR QUICK BREAK MECHANISM OF LOAD TAPCHANGING TRANSFORMER Flled Sept 20, 1955 2 Sheets-Sheet l ye. gmz

Win/2g Dec. 18, 1956 w c, SEALEY 2,774,830

CONTACT POSITIONING ARRANGEMENT FOR QUICK BREAK MECHANISM OF LOAD TAPCHANGING TRANSFORMER Filed Sept. 20, 1955 2 Sheets-Sheet 2 l fi 38a W 2|LL! M Li L l Ll 555x 4)? OCZ la /6a- /615 38G 4 36a Ag/e Momma/ UnitedStates Patent CONTACT POSITIONHWG ARRANGEMENT FOR QUICK BREAK MECHANISMOF LOAD TAP CHANGING TRANSFORMER William C. Sealey, Wauwatosa, Wis.,assignor to Allis- Chalrners Manufacturing Company, Milwaukee, Wis.

Application September 20, 1955, Serial No. 535,419

Claims. (Cl. 200-17) This invention relates in general to load tapchanging transformers and in particular to load tap changingtransformers in which the movable contacts of the tap changing switchare moved with a snap action.

In prior art tap changing systems of the general type disclosed in U. S.patent to L. H. Hill, 2,177,109, October 24, 1939, Voltage Regulator, amotor controlled in accordance with a regulated voltage and operating ata relatively slow speed, applies a force to a detent mechanism to movethe tap changing switch with an exceedingly fast snap action from oneoperating position to the next operating position.

In such systems, an extremely high potential gradient exists between theseparating contacts of the switch at the moment of circuit interruption.Such a gradient breaks down the insulating medium, which is usually oil,and the ionized medium thus presents a low resistance to current flow.The heat generated in the arc maintains the ionization until such timeas the separation of the contacts is great enough and the current fiowsmall enough to discontinue ionization of the medium.

The prior art found that if the quick moving parts of the above type tapchanger were made lighter in weight, and therefore of less inertia, thedetent mechanism would move the movable contacts of the switch from oneposition to the next with such rapidity that the are drawn at theseparating contacts would not have sufficient time to be extinguished.It was also found that if the speed of separation of the breakingcontacts were reduced to provide more arcing time, failure to extinguishthe are and consequent burning of the contacts would ensue. It wasfurther discovered that if the value of the current and voltage made andbroken by the tap changing switch in regulators of the above type wereincreased, the same problems were presented of maintaining or increasingthe speed of contact separation, while at the same time providing agreater time for extinguishing the are.

In order to overcome these problems the prior art found it desirable tomomentarily stop the movable contacts midway between the stationarycontacts. This was desirable, since higher initial breaking speeds couldbe maintained without decreasing the time available for the are to beextinguished. A system of this general type in which the movable contactis momentarily stopped midway between the stationary contacts isdisclosed in U. S. patent to W. C. Sealey, 2,560,002, July 10, 1951.

With the application of this general tap changing principle to powertransformers and step voltage regulators having relatively large currentcarrying capacities, it was found that the distance between the leadingedge of the stationary contact and the trailing edge of the movablecontact, when the movable contact was momentarily stopped, would have tobe increased if the arc was to be extinguished within a reasonable timeand without damage to the contacts. The present invention accomplishesthis increased spacing between the separating contacts Without anyincrease in the distance between stationary contacts or the size of thedial switch by extending the 2,774,830 Patented Dec. 18, 1956 auxiliarynotch, intermediate the main notches in the index plate of the detentmechanism, in the direction of movement of the movable contacts. Thisarrangement of the notches in the index plate allows the movablecontacts to be momentarily stopped at a point where the distance betweenthe leading edge of the stationary contact and the trailing edge of themovable contact is greater than has heretofore been possible to obtainin prior art devices.

It is therefore an object of the present invention to provide animproved load tap changing transformer.

Another object of the present invention is to provide in a load tapchanging transformer, an improved mechanism for changing taps with asnap action movement.

A further object of the present invention is to provide in a load tapchanging transformer having a detent mechanism for changing taps with aninterrupted snap action, an improved arrangement for momentarilystopping the movable contacts at a predetermined point to cause the areestablished at contact separation to be more readily extinguished.

Objects and advantages other than those mentioned above will be apparentfrom the following description when read in connection with the drawingsin which:

Fig. l is a View in elevation of a load tap changing transformer havinga quick break mechanism embodying the present invention;

Fig. 2 is a side view of the transformer shown in Fig. 1;

Fig. 3 is an isometric view of a portion of the detent mechanism of thetransformer shown in Figs. 1 and 2; and

Figs. 4a through 4e are diagrammatic views illustrating the improvedoperation of the load tap changing transformer shown in Figs. 1 and 2.

Referring to the drawing, the load tap changing transformer shown inFigs. 1 and 2 comprises generally a tap changing switch 11 and a detentmechanism 12. Tap changing switch 11 comprises an insulating panel 13, ashaft 14 rotatably mounted in the panel with its axis of rotation normalto the face of the panel, a plurality of stationary contact-members 15and a pair of movable contact members 16. The stationary contact members15 are spaced circumferentially on an arc of a circle having its centeron the axis of rotation of shaft 14. The movable contact members 16 arefixedly mounted with respect to the shaft 14 and are rotatable therewithin the plane of the stationary contact members 15.

Movable contact members 16 are spaced apart a distance corresponding tothe circumferential spacing of the stationary contact members 15 so thatboth movable contacts 16 may be disposed on one stationary contactmember 15 or disposed in a bridging relationship with respect to a pairof adjacent stationary contact members 15.

The detent mechanism 12 as shown comprises a stationary index plate 20supported in a plane parallel to the tap changing switch 11 by suitablesupport members 21, a shaft 23 which is rotatably journaled in thecenter of the index plate 20 with its axis normal to the plane of theplate 20, a sprocket wheel 24 which is rotatably mounted on shaft 23parallel to index plate 20, and an actuating disk 26 fixedly mounted onshaft 23 parallel to sprocket wheel 24 and spaced axially therefrom.Connecting means 25 are provided between the actuating disk 26 and themovable contacts 16 to cause contacts 16 to move in accordance with themovement of disk 26.

The detent mechanism 12 further includes means 27 for driving thesprocket wheel 24 at a relatively slow uniform speed. As shown, thedriving means 27 comprises a motor 28 and a chain 29, but other knownarrangements may be used if desired.

In order to separate the movable contacts 16 from the stationarycontacts 15 with a snap action, detent mechanism 12 further includes aspring arrangement 30 3 for converting the slow rotation of sprocketWheel 24 into a rapid snap action of the actuating disk 26, and alatching means 31 for preventing movement of the actuating disk 26 untilthe spring arrangement Stiisbiased to a'predetermined extent. Springarrangement 30 comprises a pair of spring assemblies 32, 33 spacedsymmetrically on opposite sides of shaft 23 and transverse to theaxisthe reof. Each of the spring assemblies has one end 34 connected to thesprocket wheel 24 and the other end 35 connected to the actuating disk26. The spring assemblies 32 and 33 are arranged so that the actuatingdisk 26 is in a state of balance when the mechanism '12 is deenergized.

Latch means 31 comprises a latch member 36 which has one end pivotallymounted on an edge portion of the actuating disk 26 so that the otherend extends through a suitable circumferentially elongated opening 37 inthe sprocket wheel 24. The index plate 20 is provided with a pluralityof circumferentially spaced main notches 38 which are engageable withthe portion of the latch member 36 extending through the opening 37. Themain notches 38 are disposed in index plate 20 in accordance with theoperating positions of the switch 11 so as to properly position movablecontacts 16 with respect to stationary contacts at these operatingpositions.

When a tap change is desired, the snap action movement of the movablecontacts 16 is obtained by energizing motor 28 either manually or by acondition responsive motor control circuit (not shown). Energizing motor28 causes the sprocket member 24 to rotate slowly. Rotation of sprocket24 biases the spring assemblies 32 and 33 since like ends of each ofthese assemblies are attached to the rotating sprocket while the otherends are attached to the actuating disk 26 which is prevented fromturning by the engagement of the latch member 36 in a main notch 38. Theactuating disk 26 remains fixed'until the spring assemblies 32, 33 arebiased to a predetermined extent at which time the latch member 16 iscaused to be pivoted out of engagement with main notch 33. The pivotingaction of latch member 36 is obtained by the camming action of the sides39* of the opening 37 in the sprocket 24.

The energy stored in the spring assemblies 32!, 33 at the time latchmember 36 is released causes actuating disk 26 to'move with a snapaction. Since contacts 16 move in accordance with the movement ofactuating disk 26, oneof the movable contacts 16 moves off thestationary contacts 15 quite rapidly, reducing contact deteriorationcaused by the arc established when the contacts separate. Because of therapidity at which the contacts separate and the relatively smallcircumferential spacing of the stationary contacts, means are providedto momentarily stop the movable contacts 16 to provide sufficient timefor the arc to clear itself. This means comprises an auxiliary notch 41disposed between each pair of main notches 38.

In one respect, the auxiliary notch 41 is similar to that disclosed inthe aforementioned patent to Sealey, in that the auxiliary notches serveto stop the movable contact momentarily between the stationary contacts.

However, the advantage of the present construction of the auxiliarynotch 41 over that previously suggested in the'aforementioned Sealeypatent will be readily seen by referring to Figs. 4a through 4e whichillustrate diagrammatically the structure and operation of the tapchanging switch shown in Figs. 1 and 2. In these figures stationarycontact members 150 and 15b correspond to a pair of electricallyadjacent contact members 15, movable contacts 16a and 16b correspond tomovable contacts 16, latch member 36a corresponds to latch member 36,and index plate Zita corresponds to index plate 2i Figs. 4a, 4c and 4eillustrate the position of the movablecontact members 16 with respect tothe stationary contact members 15 when the load tap changing transformeris in adjacent operating positions. Figs. 4b and 4d illustratetheposition of the movable contact at times that contacts 16 aremomentarily stopped between operating positions to provide sufficienttime for the arc to be extinguished. The operation of the mechanism whenmoved in one direction is shown from Fig. 4a through Fig. 4c, and theoperation in the other direction by Figs. 40' through 4e.

As shown in Pigspl and 4a the auxiliary notches 41 are similar to themain notches 38 except that they are extended in the direction ofmovement of the movable contacts in in order to increase the distancebetween the trailing edge 44a of contact 16b and the leading edge 45a ofcontact 15a. A similar increase in distance is obtained when contacts 16are moved in the opposite direction as shown in Fig. 4d where trailingedge 47a of contact 16]) is spaced from leading edge 48a of contact151'). By extending the latch engaging portion of auxiliary notch 41 itis possible to increase the distance separating contacts 15a and lab toa greater distance than has been obtained in the prior art withoutincreasing the size of the dial switch 11. This permits higher operatingcurrents to be handled by the switch 11 without increasing contactdeterioration due to arcing and also results in the are beingextinguished more rapidly.

It will be seen from Figs. 4a through 4e that by merely making axuiliarynotch 41a wider than the main notches 38a many advantages in operationare obtained that are not obtainable by heretofore suggested load tapchanging transformers. Besides permitting the interrupting of highercurrents, the mechanical wear on the latch 36 and index plate 26 isconsiderably reduced since the spring assemblies have a greater snubbingaction when the latch is allowed to'move past the midpoint betweenstationary contacts. This greater snubbing action also results in aquieter 'operatingmechanism since the impact speed of the latch againstthe side of the notch is decreased.

While only one embodiment of the present invention has been illustratedand described, it will be apparent to those skilled'in the art thatmodifications may be made therein without departing from the spirit ofthe invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A load tap changing transformer comprising a tap changing switchhaving a plurality of spaced stationary contacts and a pair ofcorrespondingly spaced movable contacts cooperating with said stationarycontact members to define operating positions for said transformer,detent means for switching one of said movable contacts from one of saidstationary contacts to the next with a snap action to cause said onemovable contact to be rapidly separated from said one stationarycontact, said means including a stationary index plate provided with aplurality of main notches, and a latch device movable in accordance withthe movement of said movable contacts and engageable with said mainnotches to accurately position said movable contacts with respect tosaid stationary contacts at said operating positions, and an auxiliarynotch adapted to receive said latch device to momentarily stop saidmovable contacts at a point between said operating positions whichdisposes said one movable contact further from said one stationarycontact than said next stationary contact, said auxiliary notch disposedbetween said main notches with the latch engaging portion of saidauxiliary notch extended in the direction of movement of said latchdevice.

2. A load tap changing transformer comprising a dial type changingswitch having a plurality of circumferentially spaced stationarycontacts and a pair of correspondingly spaced movable contactscooperating with said stationary contacts to define operating positionsfor said transformer, detent means for switching said movable contactsfrom one of said operating positions to the next with a snap action tocause one of said movable contacts to be rapidly separated'from'one ofsaid stationary contacts, said'detent means including a stationarycircular index plate provided with a plurality of circumferentiallyspaced main notches, and a latch device movable in accordance with themovement of said movable contacts and engageable with said main notchesto accurately position said movable contacts with respect to saidstationary contacts at said operating positions, and an auxiliary notchadapted to receive said latch device to momentarily stop said movablecontacts at a point between said operating positions which disposes saidone movable contact further from said one stationary contact than thenext said stationary contact, said auxiliary notch disposed between saidmain notches and extended circumferentially in the direction of movementof said latch device.

3. A tap changing under load transformer comprising a tap changingswitch having first and second spaced stationary contacts and first andsecond correspondingly spaced movable contacts cooperating with saidstationary contacts to define operating positions for said transformer,and a detent mechanism for moving said first movable contact from saidfirst stationary contact to said second stationary contact with a snapaction movement, said mechanism including a stationary index plateprovided with alternately arranged main and auxiliary notches, and alatch device movable in accordance with the movement of said movablecontacts and engageable with said notches to prevent movement of saidmovable contacts until said detent mechanism is biased to apredetermined extent, said main notches being disposed in said indexplate to cause said latch device to accurately position said movablecontacts with respect to said stationary contacts at said operatingpositions, said auxiliary notches disposed between said main notches tomomentarily stop said first movable contact between said first andsecond stationary contacts, the latch engaging portion of said auxiliarynotch being extended in the direction of movement of said movablecontacts to cause said first contact when momentarily stopped to bespaced further from said first stationary contact than said secondstationary contact.

4. A tap changing under load transformer comprising a tap changingswitch having first and second spaced stationary contacts and first andsecond correspondingly spaced movable contacts cooperating with saidstationary contacts to define operating positions for said transformer,a detent mechanism including a stationary index plate provided with aplurality of spaced notches, a latch device movable in accordance Withthe movement of said movable contacts and engageable with said notchesto prevent movement of said movable contacts until said detent mechanismis biased to a predetermined extent, alternate said notches beingdisposed in said index plate to accurately position said movablecontacts with respect to said stationary contacts at said operatingposition, means for biasing said detent mechanism to said predeterminedextent, means for disengaging said latch device from one of said notcheswhen said mechanism is biased to said predetermined extent to cause asnap action movement of said movable contacts, and auxiliary notchesdisposed between said alternate notches cooperating with said latchdevice to momentarily stop said first movable contact between said firstand second stationary contacts, the latch engaging portion of saidauxiliary notch being extended in the direction of movement of saidmovable contacts to cause said first movable contact when momentarilystopped to be spaced further from said first stationary contact thansaid second stationary contact.

5. A switch actuating mechanism for moving a movable contact from afirst stationary contact to a second stationary contact with a snapaction movement, said mechanism including a stationary index plateprovided with alternately arranged main and auxiliary notches, and alatch device movable in accordance with the movement of said movablecontacts and engageable with said notches, said main notches beingdisposed in said index plate to cause said latch device to accuratelyposition said movable contact with respect to said stationary contacts,said auxiliary notches disposed between said main notches to momentarilystop said movable contact between said stationary contacts, the latchengaging portion of each said auxiliary notch being extended in thedirection of movement of said movable contact to cause said movablecontact when momentarily stopped to be spaced further from said firststationary contact than said second stationary contact.

No references cited.

